In recent years, due to the excellent display effect of AMOLED (Active-matrix organic light emitting diode) displays, AMOLED displays have been highly favored at home and abroad, with related industries having developed rapidly and various pixel circuits having been successively developed. However, the ELA (Excimer Laser Annealing) progress and the Doping process for fabricating TFTs (Thin Film Transistors) in AMOLED display screen, which are used in actual production, cannot guarantee the good uniformity of TFTs, thereby there existing a Vth (threshold voltage) deviation phenomenon, which results in a deviation in the driving current obtained based on Vth. For instance, in terms of the most basic 2T1C circuits (pixel circuits each including two transistors and one capacitor) in AMOLED display screen, when same data signals are written, luminance of pixels are non-uniform, which is resulted from different Vths in the current formula. Besides, due to the wire voltage drop in the actual AMOLED display, the gate voltages of the driving transistors (DTFTs) are changed, i.e., the gate voltages of the transistors with different distances from the power source are different, thereby resulting in non-uniform luminance of the AMOLED display.